This application claims priority to Swiss Patent Application No. CH 2001 1759/01, filed on Sep. 24, 2001, the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein.
The present invention relates to a terminal covering cap for the connection terminals of a multi-phase electrical switching device with electrical connection terminals which are accommodated in an insulating housing of the switching device shared by all the phases and are equipped with clamping screws which serve for fastening electrical lines in the connection terminals, are perpendicular to the lines and are accessible from the surface of the insulating housing via recesses.
EP-A1-0051755 discloses a covering device for protecting connection terminals of electrical installation units. The covering device is approximately L-shaped in cross section. This covering device is held on the installation unit by at least one resilient lug gripping behind projections or recesses on the installation unit. This covering device serves as protection of the connection terminals against incidental contact and does not increase the electric or dielectric strength, also called xe2x80x9cvoltage strengthxe2x80x9d, between the connection terminals of neighbouring phases of the installation unit.
An object of the present invention is to provide a terminal covering cap for the connection terminals of a multi-phase electrical switching device which has the effect of increasing the electric strength between the connection terminals of neighbouring phases of the switching device and thus meets the requirements of various standards, for example the US standard UL508, with respect to the electric strength between neighbouring connection terminals of an electrical switching device, and is commercially advantageous.
The set object is achieved by providing, to ensure the electric strength between the connection terminals of neighbouring phases, an L-shaped terminal covering cap, extending with one leg over recesses leading to clamping screws and with the other leg over connection openings leading to the connection terminals. Furthermore, the L-shaped terminal covering cap closely abuts or snugly bears against the insulating housing with a negligable air gap in such a manner that it bears with its side facing the insulating housing in the edge or marginal region of said connection openings leading to the connection terminals snugly against the insulating housing, with a negligable air gap. The terminal covering cap is provided, on its surface facing away from the insulating housing, with projecting ribs between the cap openings which lead to the connection terminals. Said projecting ribs ensure the required creep distance. Various standards request testing of the electric strength between the neighbouring connection terminals of an electrical switching device. In exceptional cases, the creep distance that usually exists on the surface of the insulating material lying between the connection terminals is not sufficient to withstand the prescribed test voltage. The fact that the terminal covering cap bears on its side facing the insulating housing in the marginal region of the connection openings leading to the connection terminals snugly against the insulating housing, with a negligible air gap, has the effect of producing a barrier. Said barrier can withstand a higher test voltage, requested by various regulations, than the same distance without a terminal covering cap in bearing contact or abutting relationship according to the present invention. This measure makes it possible to increase the electric strength between neighbouring connection terminals without the creep distance being extended by enlarging the insulating housing. On the side of the terminal covering cap facing away from the insulating housing, there is sufficient space for providing ribs, so that on this side the creep distance is increased in a manner corresponding to the test voltage by means of said ribs provided between the cap openings leading to the connection terminals.
The terminal covering cap may be undetachably fastened to the finished switching device by snap connections before connecting the electrical lines. Various standards request that the terminal covering cap must be undetachably fastened to the insulating housing. This is achieved by the undetachable snap connections provided in the present invention.
The terminal covering cap advantageously has on its side facing the insulating housing at least one holding extension gripping behind in the insulating housing and at least one snap lug gripping behind a projection of the insulating housing. This arrangement makes said undetachable fastening of the terminal covering cap to the insulating housing possible without a screw connection, which is advantageous in particular in case of relatively small switching devices.
The L-shaped terminal covering cap may be screwed onto the insulating housing in the region of the recesses or openings leading to the connection terminals. The L-shaped terminal covering may be be fastened with the leg that is perpendicular theretoxe2x80x94which means with its other leg that is perpendicular to its screwed legxe2x80x94to the insulating housing by means of at least one holding stop gripping behind the insulating housing and by means of at least one snap lug engaging a projection of the insulating housing. The snap lug engaging the insulating housing provides said undetachable fastening of the terminal covering cap to the insulating housing.
The terminal covering cap may have separating extensions protruding into the cavity of the recesses leading to the connection terminals of neighbouring phases. The separating extensions extending into the cavity of the recesses which lead to the connection terminals serve as an electrical barrier and increase the limit of a minimum test voltage requested for the switching device.